This application is based upon and claims the benefit of Japanese Patent Applications No. 10-337930 filed on Nov. 27, 1998, and No. 11-192292 filed on Jul. 6, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to semiconductor devices having a movable portion inside a chip, such as a capacity type acceleration sensor, a yaw rate sensor and a pressure sensor, and having a mechanically weak structure such as an air-bridge wiring structure, and to methods of manufacturing the same.
2. Description of the Related Art
A semiconductor wafer such as a silicon wafer on which several semiconductor integrated circuit elements are formed is usually cut by a dicing-cut device for individual semiconductor chips while being disposed on an adhesivexe2x80x94sheet. The dicing-cut device requires a large amount of cutting water to remove undesirable silicon chips, radiate heat, and to facilitate the cutting.
However, when the elements to be divided include an element such as a capacity type acceleration sensor having a movable portion, or an element on which a mechanically weak structure such as an air-bridge wiring structure is exposed, such functional elements are easily broken by pressure and surface tension produced by the large amount of cutting water.
To solve this problem, JP-A-7-99172 proposes a method for dicing a silicon wafer while covering an exposed weak structure with a tape as a provisonal protective cap. The tape has an adhesive pattern to be attached to the semiconductor wafer. As a result of studies on this method, however, the following problems were found. Specifically, when the adhesive pattern is printed on the tape, a width of the pattern is, for example, 0.2 mm at least since it is limited by a mask material, printing conditions, and the like. When the tape is adhered to the semiconductor wafer, the adhesive pattern is further widended by pressure. The widened adhesive pattern may reach the exposed structure on the semiconductor wafer. When the adhesive pattern is formed with a large gap in consideration of the above problem, an area of the tape must be increased. The tape having the increased area is not suitable for an element having a reduced size. Thus, in the method desclosed in the above document, since the width of the adhesive pattern is varied when the adhesive pattern is adhered, it is difficult to securely protect the exposed structure on the wafer.
JP-A-9-27466 discloses another method for provisioanlly covering an exposed structure on a wafer with a adhesive sheet as a protective cap. The adhesive sheet is formed to have a dome portion for covering the exposed structure to prevent from being stuck to the exposed structure. This method involves difficulty for controlling the shape of the dome portion, and low productivity (through put) due to the formation of the dome portion performed by heating, and the like. Here, it should be noted that the protective caps disclosed in the documents described above protect the exposed structure not only during the dicing but also during transportation. The protective caps make the handling in the transportation easy.
The present invention has been made in view of the above problems. An object of the present invention is to provide a semiconductor device having exposed structure portions protected with a protective cap to be divided by dicing with high productivity and capable of being easily handled when transported, and to a method of manufacturing the same.
To achieve the object described above, a semiconductor device includes an adhesive sheet detachably attached to a semiconductor wafer and covering a structure portion exposed on the semiconductor wafer. The adhesive sheet is composed of a flat sheet member and an adhesive portion provided generally on an entire surface of the sheet member. The adhesive portion has a specific region facing the structure portion with an adhesion that is smaller than that of a vicinal region of the adhesive portion surrounding the specific region.
According to the present invention described above, since the adhesive sheet as a protective cap is flat, it is not necessary to form a dome portion and the like, resulting in high productivity. Since the adhesive portion is disposed generally on the entire surface of the sheet member, the adhesive portion is not widened when attached to the semiconductor wafer, and therefore, it does not invade into the structure portion. The semiconductor wafer can be diced and be transported in a state where the structure potion is securely protected by the adhesive sheet. The handling when dicing and transporting the semiconductor wafer is easy.
Preferably, the adhesive portion is made of a UV setting adhesive, an adhesion of which is reduced by UV. Accordingly, the adhesion of the specific region of the adhesive portion can be easily reduced by UV irradiation, resulting in high productivity of the protective cap.
When the semiconductor device is manufactured, the adhesive sheet can be attached to the semiconductor wafer after or before the adhesion of the adhesive portion at the specific region is selectively reduced. When the structure portion is exposed on both (first and second) surfaces of the semiconductor wafer, preferably, first and second adhesive sheets are attached to the first and second surfaces of the semiconductor wafer to cover the structure portion. The semiconductor wafer can be diced with the structure portion protected by the adhesive sheet. After that, the adhesive sheet can be easily removed by entirely reducing its adhesion.